I lost my 1st betta to unknown circumstances, and I'm dissappointed in my Girls.

"Gilly" was a $1.99 "baby betta" Petco purchase last fall. She was frisky and swam right up to me. That started the snowball known as "Betta Fever".

I started what is now an 8-fish sorority (I have 1 new girl in isolation). Gilly was always the aggressor. She earned a bad nip or 2 from her tankmates which caused her to be isolated & treated once (December).

2 days ago, her color started to fade, and she looked a little bloated. My params in their tank are perfect (exept for an 8.2 ph)and the other girls are zooming around. Gilly was hiding behind the heater. I decided the problem was social, but if she didn't turn around by today, I'd remove her.
Well, 5 minutes ago I saw all kinds of commotion in the tank. Something was attracting the 8 girls at the rear bottom of the tank. Apon inspection, all the girls were ripping Gilly to shreds, like pirahnas!

I pulled her, floated her in an emergency tank for a few minutes, but she was dead. I am shocked by the behavior of the rest of the girls! I wonder if Gilly died, or if she was bullied to death. Either way, I feel like a terrible betta mom. I have delayed moving the girls to their well-cycled, shiny 29 gallon b/c I am afraid of loss due to moving. I probably should have moved Gilly right away. My policy has always been if the fish is simply "sulking" (showing no obvious disease, is eating and moving up to the surface regularly) I "wait and see"- thinking the stress of a small hospital tank + treatment may worsen the problem.. but I will have to change my habit.

I hate saying this, but keep in mind that females are territorial just like males. So the ripping to shreds thing isn't too much of a surprise. After taking one female out, before re-acclimating her, I'd just take them all out and acclimate them all back in at once next time (regarding the hospital thing). It doesn't hurt to re-scape things as well. If you did this, regardless, the ripping thing doesn't seem to surprising. It had to have been heart-breaking to see.

My boyfriend only likes two of the soon to be eleven fish I have. One of them is a female who is soon to be part of a 6-8 fish sorority. If she was to get picked on, he would be angry at me about it.

I know they are territorial, but nothing prepares you for seeing a group of fish you picked out and love rip into another. Any non-fish-owning friend would think I was crazy to be upset!
How do I introduce all 9 girls at once? (I have 8 in the 10-gal plus 1 in a QT) I need to acclimate each fish to the new tank.